U.S. patent number 5,632,766 [Application Number 08/513,685] was granted by the patent office on 1997-05-27 for ventricular defibrillation by coordination of shocks with sensed coarse vf complexes.
This patent grant is currently assigned to Cardiac Pacemakers, Inc.. Invention is credited to William Hsu, Yayun Lin.
United States Patent |
5,632,766 |
Hsu , et al. |
May 27, 1997 |
Ventricular defibrillation by coordination of shocks with sensed
coarse VF complexes
Abstract
A method and system for ventricular defibrillation by
coordinating the delivery of defibrillation shocks with sensed
ventricular fibrillation complexes in a way which improves the
probability of success of the defibrillation shock. Ventricular
electrical activity is monitored during VF to detect coarse VF
complexes. The defibrillation shock is delivered in coordination
with the occurrence of coarse VF complexes, and specifically to
occur on the upslope portion thereof, for optimal probability of
success. Preferably, DF shock is delivered on the nth occurring
coarse VF complex, wherein n is equal to or greater than 2 and less
than or equal to about 9.
Inventors: |
Hsu; William (Circle Pines,
MN), Lin; Yayun (St. Paul, MN) |
Assignee: |
Cardiac Pacemakers, Inc. (St.
Paul, MN)
|
Family
ID: |
24044271 |
Appl.
No.: |
08/513,685 |
Filed: |
August 11, 1995 |
Current U.S.
Class: |
607/5 |
Current CPC
Class: |
A61N
1/3956 (20130101) |
Current International
Class: |
A61N
1/39 (20060101); A61N 001/39 () |
Field of
Search: |
;607/4,5 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0347708 |
|
Dec 1989 |
|
EP |
|
0550343 |
|
Jul 1993 |
|
EP |
|
0550344 |
|
Jul 1993 |
|
EP |
|
WO93/20888 |
|
Oct 1993 |
|
WO |
|
Other References
Hsia, Peng-Wie et al., "Genesis of Sigmoidal Dose-Response Curve
During Defibrillation by Random Shock: A Theoretical Model Based on
Experimental Evidence for a Vulnerable Window During Ventricular
Fibrillation," Pace, vol. 13, pp. 1326-1342, (Oct. 1990). .
Hsia, Peng-Wie et al., "Improved Nonthoractomy Defibrillation Based
on Ventricular Fibrillation Waveform Characteristics," Pace, 18, p.
803, Abstract No. 29, (Apr. 1995, Part II). .
Hsia, Peng-Wie et al., "Absolute Depolarization Vector
Characteristics Associated with Successful Defibrillation: Evidence
of a Vulnerable Period During Ventricular Fibrillation," Supplement
III Circulation, vol. 82, No. 4, p. III-738, (Oct. 1990). .
Jones, Douglas L. et al., "Ventricular Fibrillation: The Importance
of Being Coarse?," J. Electrocardiology, 17, No. 4, pp. 393-400,
(1984). .
Kuelz, Kathy W. et al., "Integration of Absolute Ventricular
Fibrillation Voltage Correlates with Successful Defibrillation,"
IEEE Transactions on Biomedical Engineering, 41, No. 8, pp.
782-791, (Aug. 1994). .
Mower, Morton M. et al., "Synchronizaton of Low-Energy Pulses to
Rapid Deflectoin Signals as a Possible Mechanism of Subthreshold
Ventricular Defibrillation," Abstracts of the 55th Scientific
Sessions, II-75, Abstract No. 298, (1982)..
|
Primary Examiner: Kamm; William E.
Assistant Examiner: Layno; Carl H.
Attorney, Agent or Firm: Schwegman, Lundberg, Woessner &
Kluth, P.A.
Claims
We claim:
1. A method of treating ventricular fibrillation, comprising the
steps of:
a) monitoring a signal representative of ventricular electrical
activity during a period of ventricular fibrillation;
b) detecting in the monitored signal, the occurrence of coarse VF
complexes;
c) analyzing coarse VF to determine upslope; and
d) delivering a DF shock during the upslope portion of a
complex.
2. A method according to claim 1, including the step of counting
occurrences of coarse VF complexes, and coordinating the delivery
of the DF shock with the upslope of a predetermined numbered
occurrence of coarse VF complex.
3. The method of claim 1 wherein the step of monitoring comprises
monitoring the morphology signal, across proximal and distal
shocking coils of an endocardial lead, and wherein the step of
delivering a DF shock includes applying a pulse of electrical
energy to the endocardial lead.
4. The method of claim 1 wherein the steps of detecting and
analyzing the occurrence of a coarse VF complex includes sensing
when the amplitude of the VF signal is greater than a predetermined
value with a positive slope or rate of change.
5. The method of claim 1 wherein the step of delivering a DF shock
includes timing the shock based on when the amplitude of the VF
signal is greater than a predetermined value and has a positive
slope or rate of change.
6. A method of treating ventricular fibrillation, comprising the
steps of:
a) monitoring a signal representative of ventricular electrical
activity during a period of ventricular fibrillation;
b) detecting and counting the occurrence of coarse VF complexes;
and
c) delivering a DF shock during the nth counted complex, where n is
a number greater than or equal to 2 and less than or equal to about
9.
7. The method of claim 6 wherein the step of monitoring comprises
monitoring the morphology signal, between proximal and distal
shocking coils, of an endocardial lead, and wherein the step of
delivering a DF shock includes applying a pulse of electrical
energy to the endocardial lead.
8. The method of claim 6 wherein the step of detecting the
occurrence of a coarse VF complex includes sensing when the
amplitude of the VF signal is greater than a predetermined value
with a positive slope or rate of change.
9. The method of claim 6 wherein the step of delivering a DF shock
on the nth complex includes timing the shock based on when the
amplitude of the VF signal is greater than a predetermined value
and has a positive slope or rate of change.
10. A method of treating ventricular fibrillation, comprising the
steps of:
a) monitoring a signal representative of ventricular electrical
activity during a period of ventricular fibrillation;
b) detecting the occurrence of coarse VF complexes;
c) analyzing coarse VF complexes to determine upslope; and
d) delivering a DF shock during the upslope of the nth counted
complex, where n is a number greater than or equal to 2 and less
than or equal to about 9.
11. A method according to claim 10 wherein the step of analyzing
includes counting coarse VF complexes.
12. The method of claim 10 wherein the step of monitoring comprises
monitoring the morphology signal, between proximal and distal
shocking coils, of an endocardial lead, and wherein the step of
delivering a DF shock includes applying a pulse of electrical
energy to the endocardial lead.
13. The method of claim 10 wherein the steps of detecting and
analyzing the occurrence of a coarse VF complex includes sensing
when the amplitude of the VF signal is greater than a predetermined
value with a positive slope or rate of change.
14. The method of claim 10 wherein the step of delivering a DF
shock on the nth complex includes timing the shock based on when
the amplitude of the VF signal is greater than a predetermined
value and has a positive slope or rate of change.
15. A method of determining when to deliver a DF shock to a heart
in ventricular fibrillation, comprising the steps of:
a) monitoring a signal representative of ventricular electrical
activity during a period of ventricular fibrillation;
b) detecting the occurrence of coarse VF complexes as intervals of
increase of the absolute value of the monitored signal; and
c) selecting the time for DF shock delivery based on when the
absolute value of the monitored VF signal reaches a predetermined
value during a period of increasing rate.
16. A method of determining when to deliver a DF shock to a heart
in ventricular fibrillation, comprising the steps of:
a) monitoring a signal representative of ventricular electrical
activity during a period of ventricular fibrillation;
b) measuring the amplitude of the monitored signal;
c) determining the rate of change of the amplitude of the monitored
signal; and
d) selecting the time for DF shock delivery based on the amplitude
of the monitored signal, a predetermined value during fibrillation,
and whether the rate of change of the amplitude is positive.
17. A method of claim 16 wherein the step of measuring includes
repeated sampling of the monitored signal, and the step of
determining rate of change includes comparing samples of the
monitored signal over a small increment of time.
18. A method of treating ventricular fibrillation, comprising the
steps of:
a) monitoring a heart signal representative of ventricular
electrical activity;
b) detecting the presence of ventricular fibrillation
c) during VF, detecting the occurrence of coarse VF complexes by
measuring the monitored signal; and
d) for the nth coarse VF complex, where n is greater than or equal
to 2 and less than or equal to 9, delivering a coordinated DF shock
based on the a predetermined value for the amplitude of the
monitored signal, and whether the amplitude has a positive the rate
of change.
19. A method according to claim 10 further including the step of
delivering at least one asynchronous DF shock if the VF is not
terminated by the delivery of coordinated DF shocks.
20. A defibrillator, comprising:
a lead system for placement in electrical contact with the
ventricle of the heart;
a sensing system, attached to the lead system for monitoring
ventricular electrical activity, which detects the presence of VF,
and during VF to detect coarse VF complexes;
a DF control system for controlling delivery of DF shocks through
the lead system to the ventricle, the control system responsive to
the sensing system to deliver a DF shock when the sensed VF complex
increases to a predetermined value with a positive rate of
change.
21. The defibrillator according to claim 20 wherein the DF control
system comprises a counting subsystem which counts the occurrence
of VF complexes, and the DF control system delivers a DF shock
coordinated with the nth coarse complex, where n is greater than or
equal to 2 and less than or equal to about 9.
22. The defibrillator according to claim 21 wherein the DF control
system delivers the coordinated shocks during an interval following
onset of VF, and at least one asynchronous DF shock if the VF is
not terminated by the coordinated shocks.
Description
FIELD OF THE INVENTION
This invention pertains to the field of treatment of ventricular
fibrillation by the delivery of electric defibrillation shocks. In
particular, the invention pertains to a method and system for
coordinating the delivery of defibrillation shocks with sensed
ventricular fibrillation complexes in a way which improves the
probability of success of the defibrillation shock.
BACKGROUND OF THE PRIOR ART
Electric shock defibrillation is a proven technique of treatment of
the serious and immediately life-threatening condition of
ventricular fibrillation (VF). For patients known to be at risk, an
implantable defibrillator may be used. Such devices contain an
energy source, an electrode lead system in contact in the heart, a
sensing system to detect the onset of fibrillation, and a pulse
generator for delivering the defibrillation (DF) shock. Often they
are combined with a pacemaker function in the same device.
Existing devices are generally designed or programmed to deliver a
shock or series of shocks at a fixed interval or intervals
following the detection of the fibrillation, unless fibrillation
spontaneously terminates on its own first, or until recovery is
achieved, as evidenced by the resumption of normal ventricular
rhythm. The amount of energy to be delivered in a shock must be
carefully chosen. If too small, it may not be successful in
terminating the fibrillation. 0n the other hand, the shock must not
be too large, from physiological considerations, and also in
consideration of the limited energy storage in an implanted
device.
It is also known in the treatment of tochyarrhythmia to use an
implantable atrial defibrillator to deliver pulses of
defibrillating energy to the atria synchronized with sensed R waves
of the ventricle. However, in the case of VF, there is not an R
wave to synchronize to, so the DF shock must be delivered
asynchronously.
It is known that ventricular electrical signals during fibrillation
may exhibit a pattern, known as "fine VF," characterized by
relatively low signal amplitude and lack of organized features; and
they may also exhibit a pattern known as "coarse VF," subjectively
characterized by intervals of higher amplitude, which may repeat,
separated by fine VF intervals. It has also been suspected that it
is easier to defibrillate coarse VF than fine VF. Because of this,
previous works have suggested the possibility of timing of DF
shocks to features of the VF waveforms as a way to improve DF
efficacy. However, it has not been clear from such prior works,
which features are important, and how to detect and coordinate to
them.
One experimenter retrospectively noted diastolic periods in the
monophasic action potential (MAP) tracings, and suggested these
periods were more conducive to defibrillation. Another
retrospectively observed that some subthreshold defibrillations
which were successful had a fixed timing relationship with a
bipolar sensing signal in the right ventricle of dogs. However,
another study examined spatial coherence in VF on surface of heart
using epicardial sensing electrodes, and concluded that coarseness
and fineness of VF was mainly due to lead orientation, and not to
the degree of organization of electrical activity as measured.
Therefore, there appears to be no firm correlation per se
recognized in the prior art between DF shock timing and VF
features, especially one that may be successfully applied
prospectively. One recent study retrospectively examined the
correlation between the voltages measured on the surface leads and
the energy required to defibrillate dogs instrumented with
epicardial patches. Some reduction in energy requirements was found
with defibrillation shocks that happened at places where measured
voltages were "high."
It is clear that while a number of investigators have pointed to
the possibility of using VF waveform features as a guide to
delivering DF shocks, there are problems to be solved in the
practical and effective prospective detection of VF features, and
the determination of which features thereof are significant, in
terms of coordination of DF shocks, for maximizing efficacy.
SUMMARY OF THE INVENTION
As explained in detail below, we have provided an improved method
and system for detecting an optimal timing for the delivery of
shocks, such that the shocks delivered have an improved probability
of success in terminating the fibrillation. This improved efficacy
provides important medical advantages to the patient, both in the
greater probability of success of individual shocks, and also in
the reduction in pulse energy and number of shocks needed to
defibrillate. The method and system of the invention is based in
part on the detection of characteristics of coarse VF complexes
which may exist during fibrillation, and the coordination of DF
shocks with portions of those complexes.
To overcome the problems in the prior art, the present invention
provides an improved method and system for detecting coarse VF
complexes, and for coordinating the delivery of DF shocks.
According to one feature of the invention, ventricular electrical
activity is monitored during a period of ventricular fibrillation,
and the occurrence of coarse VF complexes is detected. A favorable
instant of time for delivery of a DF shock is selected when the
magnitude or absolute value of the monitored VF signal reaches a
predetermined value during a period of increasing signal. In this
way the DF shock may be coordinated with the upslope portion of a
VF complex.
According to another feature of the invention, the nth occurring
coarse VF complex is selected for the coordinated DF shock, where n
is equal to 2 or more, and less than or equal to about 9. As a
practical matter, the coordinated DF shock should be delivered
prior to that count, because of the time element.
According to another aspect of the invention, an improved
defibrillator system includes a lead system for placement in
electrical contact with the ventricle of the heart and a sensing
system attached to lead for monitoring ventricular electrical
activity. The sensing system detects the occurrence of VF, and
during VF, also detects coarse VF complexes. The system includes a
controlled DF pulse generator for delivering DF shocks to the lead
system to the ventricle. A control system for controlling the pulse
generator, operates in responsive to the sensing system and
triggers the DF pulse generator to deliver a DF shock when the
sensed VF complex increases to a predetermined value with a
positive rate of change. In this manner, the DF shock is
coordinated with the upslope of a VF complex, which we have found
will substantially improve the probability of success of the DF
shock.
According to a preferred form of this system, control system is
operative to count the occurrence of VF complexes, and to trigger
delivery of a DF shock coordinated with the nth coarse VF complex,
where n is equal to or greater than 2 and less than or equal to
about 9. If success in not achieved with coordinated DF shocks, the
system switches to asynchronous shocks.
These and other features and advantages of the invention will
become apparent from the following description of the preferred
embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of an implantable defibrillator/pacemaker
of the type with which the present invention may be implemented,
including a diagrammatic representation of a lead system placed in
a heart;
FIG. 2 is a flow chart illustrating a mode of operation of the
defibrillator/pacemaker of FIG. 1 in detecting tochyarrhythmia and
VF;
FIG. 3 is a waveform of a morphology signal from a heart in VF;
FIG. 4 is a flow chart illustrating the computation of Standard
Amplitude of Morphology (SAM) by the system;
FIG. 5 is a flow chart illustrating the operation of the invention
for delivering DF shocks coordinated with a VF feature; and
FIG. 6 is a waveform of a morphology signal from a heart showing
fine VF and coarse VF complexes, and illustrating the delivery of
the DF shock coordinated with a VF feature.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The preferred embodiment of the invention is illustrated herein as
included in an implantable heart defibrillator/pacemaker, which may
include numerous pacing modes as is generally known in the art. The
system and method of the invention could also be implemented in an
external defibrillator/monitor.
In FIG. 1, defibrillator/pacemaker 10 is shown in block diagram
form. It includes terminals, labeled with reference numbers 11, 12,
13, and 14, for connection to a lead system 20. Lead system 20 is
preferably an endocardial lead, although other types could also be
used within the scope of the invention. An endocardial lead is
adapted for placement in the right ventricle. The lead system
includes a number of electrodes or electrical contacts. The tip
electrode 21 is at the distal end of the lead system, and connects
electrically through a conductor provided in the lead, for
connection to terminal 11. Lead system 20 also includes an RV coil
electrode 22 space near the distal end for placement in the right
ventricle, and this RV coil electrode connects through internal
conductors in the lead and is connected both to terminals 12 and
13. The lead system 20 also includes an SVC electrode 23,
positioned a distance back from the distal end of the electrode as
indicated. The SVC electrode is connected to terminal 14.
The defibrillator/pacemaker 10 is a programmable
microprocessor-based system, with a microprocessor indicated by
reference number 30. Microprocessor 30 operates in conjunction with
a memory 32, which contains parameters for various pacing and
sensing modes. Microprocessor 30 includes means for communicating
with an internal controller, in the form of an RF
receiver/transmitter 34. This includes a wire loop antenna 35,
whereby it may receive and transmit signals to and from an external
controller 36. In this manner, programming inputs can be applied to
the microprocessor of the defibrillator/pacemaker after implant,
and stored data on the operation of the system in response to
patient needs can be read out for medical and analysis.
In the defibrillator/pacemaker of FIG. 1, the tip and RV coil,
connected through leads 11 and 12, are applied to a sense amplifier
15, whose output is shown connected to an R wave detector 16. These
components serve to amplify and sense the QRS wave of the heart,
and apply signals indicative thereof to a microprocessor 30. Among
other things, microprocessor 30 responds to the R wave detector 16,
and provides pacing signals to a pace output circuit 17, as needed
according to the programmed pacing mode. Output circuit 17 provides
output pacing signals to terminals 11 and 12, which connect as
previously indicated to the tip and RV coil electrodes, for normal
pacing.
The DF portion of the defibrillator/pacemaker FIG. 1 includes a
high energy output pulse generator 40, which operates under the
control of microprocessor 30, as indicated. Pulse generator 40 is
connected to terminals 13 and 14, which connect to the RV coil and
SVC as previously mentioned. In this manner, DF shocks can be
provided through the endocardial lead system 20 for defibrillation
when called for by the microprocessor, and specifically the
software implementation of control algorithms.
FIG. 2 illustrates overall modes of operation of the system. In
paced operation, the system operates under programmed control to
monitor heart beats occurring in the patient's heart. This is
indicated by block 100 in FIG. 2. As is generally known in the art,
such monitoring is accomplished through the sense amp and R wave
detector, elements 15 and 16 in FIG. 1, and microprocessor control.
Pacing may be administered as needed, depending upon the type of
pacing functions provided in the defibrillator/pacemaker.
Decision block 102 tests whether a tochyarrhythmia has been
detected. This is done through analysis of electrical signals from
the heart under control of the microprocessor and its stored
program. If such condition is not detected, control branches via
path 103 back to the heart beat monitor block 100, and the process
continually repeats.
If, however, a tachycardia arrhythmia condition is detected at
decision block 102, control passes via path 105 to decision block
106, which tests for VF, through analysis of heart signals as is
known in the art. If VF is not detected, control branches to block
108 for VT therapies, as is known in the art.
If at block 106, VF is detected, control branches to the VF
therapies of FIGS. 4 and 5, which include coordinated DF shocks
according to the present invention, as described in greater detail
below.
FIG. 3 illustrates a morphology signal such as would be detected by
sensing amp 18, from the signal appearing across the RV coil-SVC in
an endocardial lead. For other types of lead systems, similar or
corresponding signals would be present. In FIG. 3, the wave form is
the voltage signal at the sense amp 18. The vertical axis
represents amplitude, and the horizontal axis represents time. As
used herein, the heart (morphology) signals are represented as what
is considered as normal polarity of signals from the heart. Thus,
references to increasing signal, positive slope, or upslope, are
all with reference to normal polarity. Reversing the polarity of
the leads would cause reversal of the polarity of the signal, in
which case a corresponding reversal of positive slope to negative
slope. If the polarity of sensing is changed, the system could
coordinate DF shocks on negative-going signals, but the data to
date suggests this might not be as effective. Alternatively, the
absolute value of the sensed signal could be used, which would
correspond to either positive or negative polarity signals. For
purposes of the preferred embodiment, positive or normal polarity
will be assumed.
In FIG. 3 Zones F1 and F2 show regions of fine VF. Zones C1 and C2
show coarse VF complexes. Within complex C1, a single peak feature
of the complex is indicated by reference number 50. The difference
in amplitude between the amplitude extremes, 52, 51, indicates the
peak-to-peak amplitude calculation which is used as a part of the
method of the invention.
In FIG. 4, the symbol "1" in the circle is the link from FIG. 2.
Upon occurrence or detection of a VF condition, the Standard
Amplitude of Morphology (SAM) is computed for a five-second
interval. The five seconds is programmable, and a different value
may be used. At block 120, which is reached after a VF has been
detected in FIG. 2, a time is initialized at a starting or zero
point. Flow in branches to step 122, where the SAM is computed,
based upon peak-to-peak value readings, as indicated in FIG. 3.
Preferably, this is accomplished by continually taking samples of
the morphology signals and comparing them with previously obtained
samples. When such comparison shows a trend reversing, i.e., from
decreasing to increasing, or from increasing to decreasing in
value, a bottom or top, i.e., a peak, negative or positive, has
been reached. Such peak values are then stored for comparison with
other peak values as part of the SAM calculation. For each peak
occurring in a complex, the high and low values, and hence the
peak-to-peak values, are calculated and stored.
Flow then proceeds to decision block 124, where the time for this
five-second interval is tested. If the five seconds (or other
programmable interval) has not passed, flow branches back via path
125 to the computation block 122, and computation detection of
peaks and computation of peak-to-peak value continues. If, however,
the time has exceeded or equaled the five-second set interval,
control passes to block 126. At this point, the SAM is calculated,
as being the average of the five largest peak-to-peak measurements
during the five-second interval in FIG. 4. This is done through
recall, comparison, and calculation based upon the stored peak
values.
FIG. 5 shows the operation of the system for delivering coordinated
DF shocks based on sensed VF complex features. The start of FIG. 5
is reached from the flow chart of FIG. 4. At step 140 n (the count
for CMC discussed below) is set to zero, the waiting period is
initialized, and the waiting period timer is started. This defines
the time period during which coordinated DF shocks may be
attempted, and after which the system will switch to asynchronous
DF shocks. This time period is preferably programmable as one of
the programming parameters for the defibrillaor/pacemaker 10
microprocessor. This time period must be kept within reasonable
physiological limits, before going to asynchronous mode. For
example, a period of 10 seconds may be appropriate. Decision block
142, which potentially is looped through multiple times, tests
whether the waiting time limit programmed for coordinated DF shocks
has passed. If not, control passes to step 144, where the amplitude
of the morphology signal for the present or current point is taken
by sense amp 18. This could be done by hardware or software in
analyzer 19, part of which could also be done by software in
microprocessor 30.
The amplitude of the current point is compared to the previously
computed value of SAM, at step 144. If it has a peak-to-peak
amplitude greater than or equal to 50% of SAM, it is identified as
a Candidate Morphology Complex (CMC), and a count of CMC is
incremented by one. The CMC count n is tested at step 146. If the
count is equal to or above the programmed number (which is 2, in
FIG. 5, but which could be changed by programming the system),
control passes to step 148. If not, control returns to path 147 and
the start of the sequence.
At step 148 the system tests whether the current point is on an
upslope, i.e. has a positive slope. This is done by comparing the
amplitude of the current point to the amplitude of the previous
point, to determine the trend.
Step 150 then tests whether the current point is at greater than
50% of the SAM value, and has a positive slope. If either of these
is not met, then control branches to path 147, to repeat the loop.
If both of these conditions are met, then control passes to step
152. Also, if the waiting period had timed out in step 142, without
finding the required conditions for coordinated DF shocking, then
control would have passed via path 143 to step 152, also.
At step 152, the system tests whether the stored energy in the high
energy output 40 has reached the pre-programmed level. It may take
several seconds to do so, depending on the set level and the
battery condition. If the energy level has not been reached,
control passes via 147 to loop again. After the energy level has
been reached at step 152, control passes to step 160, which causes
the DF pulse generator 40 to deliver the DF shock.
This is illustrated in the waveform of FIG. 6, which is a
morphology signal similar to FIG. 3. The zone labelled F is a area
of fine VF, and the zone C is a coarse VF complex. As the VF is
occurring in real time, the system is sensing and monitoring the
morphology signal. After the first major peak indicated the system
has determined that a peak of a possible coarse VF complex has
occurred, and the count is incremented at the peak "n=2". Assume,
as is the case in FIG. 6, that it is in fact the start of a VF
complex. The second peak "n=2"is counted as 2. On the next upslope,
as the amplitude passes 50% of the Standard Amplitude of Morphology
(SAM), on a CMC peak count of 2 or more, and with a positive slope,
and if there is sufficient energy at step 152, the decision is made
based on these criteria to deliver the DF shock. The microprocessor
30 and pulse generator 40 then deliver the shock shortly thereafter
based on this decision. The DF shock is indicated at line 162.
Following the delivery of the DF shock, the sensing circuits of the
defibrillator/pacemaker check to see whether the shock was
successful, that is, whether the VF has stopped. This is
represented by a return to point "0"at the start of FIG. 2. If not
successful, and if VF continues, this is detected in FIG. 2, and
control passes again to FIG. 5 to repeat the VF therapy. The
waiting period (steps 140, 142) for the second or higher passes can
preferably be by-passed (or at least separately programmed from the
first pass). Then if the first shock fails, the process of sensing
and coordination for delivery for a second shock can begin
immediately.
* * * * *